Human Trail R1, CD261 or DR4 (Death Receptor 4) is a TNF receptor, which is a receptor for Trail (APO2 ligand). Trail R1 is involved in apoptosis. In the Trail receptor family, Trail R1, but also Trail R2 (DR5) transduce an apoptosis signal, whereas Trail R3 (DcR1) and Trail R4 (DcR2) antagonize TRAIL-induced apoptosis. Binding of trimeric Trail to Trail R1 induces apoptosis by oligomerization (likely to be trimerization) of the receptor. Trail R1 cDNA encodes a 468 amino acid residue precursor protein containing extracellular cysteine-rich domains, a transmembrane domain and a cytoplasmic death domain. Trail R1 shares 55% of its amino acid sequence with Trail R2. Trail R1 is widely expressed in normal tissue.